This invention relates to an ignition coil unit for an internal combustion engine and, more particularly, to an ignition coil unit in which an ignition coil and a power switch for controlling a primary current through the ignition coil are integrally combined into a unit.
FIG. 4 is an electrical circuit diagram of a known ignition coil unit for an internal combustion engine. The ignition coil unit comprises an ignition coil A having a primary winding 2 and a secondary winding 6, and a power switch circuit B having a plurality of electric and electronic circuit components. In FIG. 4, it is also seen that an electric source C and an ignition signal control circuit D are connected to the ignition coil unit.
The power switch circuit B comprises a power transistor 1 for switching a primary current flowing through the primary winding 2 of the ignition coil A, a current limiting circuit 4 and a current detecting circuit 3 for detecting a potential difference generated by the primary current and for transmitting a primary current control signal to the current limiting circuit 4.
FIG. 5 is a front view of the known ignition coil unit before it is filled with insulating resin, and FIG. 6 is a sectional side view of the ignition coil unit illustrated in FIG. 5 in which the ignition coil A and the power switch circuit B are integrally combined. In FIGS. 5 and 6, the secondary winding 6 of the ignition coil A is disposed within a casing 5 and concentrically wound around the primary winding 2 of the ignition coil A and an iron core 7. Thus, the ignition coil A is composed of the primary winding 2, the secondary winding 6 and the iron core 7. The iron core 7 is substantially C-shaped member having a pair of substantially U-shaped members welded together at an end of one of the legs of the U positioned in an opposing relationship. An air gap 7a is defined between opposing legs of the U-shaped members. One leg 7b of each of the U-shaped members is much longer than the other leg 7c and the air gap 7a is not centrally located with respect to the ignition coil A. A heat dissipating plate 22 made for example of aluminum is disposed in the casing 5 and a packaged power switch circuit 23 having the power switch circuit B therein is attached to the heat dissipating plate 22. The packaged power switch circuit 23 comprises a mold resin, 23a hermetically sealing and packaging the power switch circuit B into a single unitary piece by the transfer molding. A connector 8 is integrally molded with the casing 5. As illustrated in FIG. 6, an electrically insulating resin 9 is filled within the casing 5.
As seen from FIGS. 5 and 6, the connector 8 has a plurality of connector terminals 11, 13, 15, 18. The first connector terminal 11 is electrically connected to the one end of the secondary winding 6 through a secondary winding ground line 10 and the second connector terminal 13 is electrically connected to the one end of the primary winding 2 through a source line 12. The third connector terminal 15 is electrically connected to a base terminal 16 of the power transistor 1 (See FIG. 4) in the power switch circuit B within the packaged power switch circuit 23 through a control signal line 14. The fourth connector terminal 18 is electrically connected to a ground terminal 19 of the power switch circuit B through a ground line 17. A collector terminal 21 of the power transistor 1 is electrically connected to the other end of the primary winding 2 through a collector line 20.
In the known ignition coil unit as described above, the primary current of the primary winding 2 flows through the current detection circuit 3, where the current level is detected as the potential difference upon which a control signal is supplied to the current limiting circuit 4. The current limiting circuit 4 controls the primary current flowing through the primary winding 2 of the ignition coil A in accordance with this control signal. In response to this primary current flowing through the primary winding 2, a high voltage to be supplied to a distributor (not shown) is generated in the secondary winding 6 of the ignition coil A.
With the known ignition coil unit as described above, after the packaged power switch 23 and the primary and secondary windings 2, 6 are mounted within the casing 5, electrical connections such as the connections between the connector terminals 11, 15, 18, 13 of the connector 8, the primary and secondary windings 2, 6 of the ignition coil A and the power switch circuit B must be provided through separate electrical conductors 10, 12, 14, 17, 20 within the limited space in the casing 5. Therefore, the ignition coil unit cannot be easily and speedily assembled, and these connecting portions sometimes fail to be tightly and correctly connected, and thus may be easily damaged.